Wood Modification Research Articles

Hybrid Approach for Wood Modification: Characterization and Evaluation of Weathering Resistance of Coatings on Acetylated Wood

Wood, as a biological material, is sensitive to environmental conditions and microorganisms; therefore, wood products require protective measures to extend their service life in outdoor applications. Several modification processes are available for the improvement of wood properties, including commercially available solutions. Among the chemical treatments, acetylation by acetic anhydride is one of the most effective methods to induce chemical changes in the constitutive polymers at the cellular wall level. Acetylation reduces wood shrinkage-swelling, increases its durability against biotic agents, improves UV resistance and reduces surface erosion. However, even if the expected service life for external cladding of acetylated wood is estimated to be 60 years, the aesthetics change rapidly during the first years of exposure. Hybrid, or fusion, modification includes processes where the positive effect of a single treatment can be multiplied by merging with additional follow-up modifications. This report presents results of the performance tests of wood samples that, besides the modification by means of acetylation, were additionally protected with seven commercially available coatings. Natural weathering was conducted in Northern Italy for 15 months. Samples were characterized with numerous instruments by measuring samples collected from the stand every three months. Superior performance was observed on samples that merged both treatments. It is due to the combined effect of the wood acetylation and surface coating. Limited shrinkage/swelling of the bulk substrate due to chemical treatment substantially reduced stresses of the coating film. Hybrid process, compared to sole acetylation of wood, assured superior visual performance of the wood surface by preserving its original appearance.

Thermal behavior and decay performance of wood modified with poly(ethyl cyanoacrylate)

ABSTRACT Ethyl cyanoacrylate polymerizes at room temperature, and is often used as an adhesive in many areas for a wide variety of applications. In this study, the possibility of using poly(ethyl cyanoacrylate) in the field of wood modification was investigated. For this purpose, Scots pine (Pinus sylvestris L.) and Oriental beech (Fagus orientalis) samples were impregnated with poly(ethyl cyanoacrylate) that was synthesized using acetone. Modified samples were characterized by Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Scanning Electron Microscopy (ESEM). Decay performance was done with white rot fungus (Trametes versicolor (L: Fr.) Pilat. (FFPRI 1030)) for beech wood and brown rot fungus Coniophera puteana for pine wood; the European standard EN113 FTIR analysis indicated that PECA could appreciably alter the chemical structure in modified wood. Thermal changes in modified wood were be minor compared to those of untreated wood. Samples treated with PECA had significantly lower mass losses than untreated samples as a result of fungal exposure to Coniophora puteana and T. versicolor.

Poly(ε-caprolactone) grafting into Scots pine wood: improvement on the dimensional stability, weathering and decay resistance

Wood modification treatments by substitution or blocking of wood hydroxyl groups with hydrophobic molecules are some of the novel approaches that may improve dimensional stability, weathering and decay resistance of wood. In this study, the Scots pine (Pinus sylvestris L.) wood was modified by ring opening polymerization of e-caprolactone to investigate the artificial weathering and decay resistance. In total, 672 h of artificial weathering was applied on modified wood by exposure of UV-light and water cycles. Additionally, decay test was carried out by using Coniophora puteana and Trametes versicolor fungi on the samples after leaching procedure. After weathering, the color change and contact angle measurements, as well as macroscopic observations revealed that the modified wood had significantly better surface properties than reference wood. FT-IR and SEM analysis proved that there was still polycaprolactone on the weathered surface with some minor crack formations of wood structure. The polycaprolactone modification effectively protected wood against decay even after leaching. This study also demonstrates that the polycaprolactone modification can provide a significant improvement on dimensional stability, as well as water repellence of Scot pine wood.

Wood modification with N-methylol and N-methyl compounds: a case study on how non-fixated chemicals in modified wood may affect the classification of their durability

Abstract Chemical modification is increasing the durability of wood against biological deterioration. Usually, the effect of a new treatment on the durability of wood is screened in laboratory decay tests, where durability classes are assigned on the basis of the mass loss (ML) caused by degrading fungi. The aim of this study was to demonstrate how non-fixated chemicals in modified wood may affect fungal ML measurements and corresponding durability classification when wood samples are incubated under humid conditions for long periods. Wood blocks were treated with solutions of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU), methylated DMDHEU (mDMDHEU) and 1,3-dimethyl-4,5-dihydroxyethyleneurea (DMeDHEU) and subjected to consecutive cold-water leaching cycles. Significant amounts of non-fixated chemicals were removed from the wood by three leaching cycles and might lead to ML mistaken as response of fungal decay. Consequently, the treated material was assigned erroneously by up to four durability classes (DC) worse than material which did not include leachable, non-fixated chemicals. Thus, for a reliable durability classification of chemically modified wood, prolonged leaching procedures are recommended to assure that the measured ML is entirely attributed to fungal decay.

Pine wood modification via an antifungal oil – Heat treatment and its effect on annual wood rings

Thyme oil, which is an anti-fungicide, was used to increase the physical and mechanical properties of wood as well as improve its strength, especially in outdoor conditions. For this purpose, Stone pine (Pinus pinea L.) wood samples classified according to the annual number of rings were exposed to either the impregnation process or the combined process, which was comprised of impregnation followed by heat treatment. As a result of the study, it was determined that the wood had different physical and mechanical properties based upon the number of annual rings. In addition, it was specified that the thyme oil used in the impregnation process improved the physical properties of the wood and also reduced the water absorption during the combined process. As a general conclusion, the impregnation process and the combined process increased the mechanical properties of the wood in parallel with an increase in the number of annual rings. The process of impregnation of wood materials with thyme oil is promising due to its anti-fungal and antibacterial properties, its ability to be used in small amounts in on-site impregnation, and it being an environmentally friendly product for the wood protection industry.

Potentials of silicate-based formulations for wood protection and improvement of mechanical properties: A review

Silica or silica-precursor systems are attractive for the protection of wood against biotic and abiotic damages and for improvement of the fire resistance. Alkali metal silicate solutions, also known as water glasses, colloidal silica (nanosilica dispersions) and other inorganic–organic hybrids resulting from the sol-gel chemistry of alkoxysilane compounds, are products available for this purpose. These chemicals are increasingly considered to formulate wood modification products or to develop surface coatings. This review article is focused on in-depth treatments of wood through dipping, soaking or vacuum-pressure impregnation methods. The techniques used to convert monomers and low molecular weight silicate species in water glasses into less soluble and leaching-resistant silica particles, such as heat treatment, acid treatment and reactions with multivalent metal cation salts, are discussed. The similarities and differences between the various raw-impregnation materials and the properties of the final products are highlighted. Water glasses after appropriate curing, colloidal silica and tetraalkoxysilane-based formulations all lead to deposition of silica particles (SiO2) at the surface of the cell walls, in lumens and pores. Low molecular weight organosilanes and other organo-modified formulations that are able to penetrate the wood cell walls and react with wood components are good dimensional stabilizers. The treated wood exhibits, in general, increased mechanical properties (strength, hardness) and improved resistance to biodegradation and fire retardancy. The efficiency of the treatments can significantly be enhanced to a level fulfilling the requirements for industrial applications by the addition of biocides, ultraviolet absorbers or antioxidants, fireproofing compounds (boron or phosphorus-based compounds, multivalent metal salts) and hydrophobic alkylalkoxysilanes. Silica acts as a barrier/support to many of these additives preventing them from leaching.

A thermal modification technique combining bulk densification and heat treatment for poplar wood with low moisture content

This study aimed to obtain the most suitable process parameters of the bulk densification and heat treatment for the modification of poplar wood with a moisture content of approximately 3–5%. Based on the heat-mass transfer model, the best preheating temperature and time for the bulk densification process were 180 °C and 361 s, respectively. The optimal heat treatment temperature and time were 190 ℃ and 3 h, respectively. The resultant wood samples exhibited the highest storage modulus and the lowest loss factor, indicating that this kind of wood product has a long service life, suitable for solid wood flooring applications.

Dynamic strength properties and structural integrity of wood modified with cyclic N-methylol and N-methyl compounds

Abstract Cyclic N-methylol compounds have been used for cell wall impregnation modifications of wood. Besides an improved decay resistance and dimensional stability, the modifications resulted in a decrease of wood’s dynamic strength properties. However, the mechanisms behind a significant loss in dynamic strength are not fully understood yet. In this study, wood blocks were treated with the N-methylol compounds 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and methylated DMDHEU (mDMDHEU) and the N-methyl compound 1,3-dimethyl-4,5-dihydroxy-ethyleneurea (DMeDHEU). In order to study the factors that control the changes of wood performance under dynamic loads, single (impact bending strength, IBS) and multiple dynamic impact (resistance to impact milling, RIM) tests were applied. It became evident, that reductions in IBS and RIM increased with increasing solid content, formaldehyde content and catalyst concentration of the impregnation solutions, but were not affected by a cold-water leaching. Differences in structural integrity of wood modified with N-methylol and N-methyl compounds were more pronounced than those of IBS. Therefore, RIM appeared more sensitive to changes on cellular level, as a higher degree of co-condensation of the N-methylol compounds with cell wall polymers was expected in comparison with the N-methyl compound.

Lignin and Lignin-Derived Compounds for Wood Applications-A Review.

Improving the environmental performance of resins in wood treatment by using renewable chemicals has been a topic of interest for a long time. At the same time, lignin, the second most abundant biomass on earth, is produced in large scale as a side product and mainly used energetically. The use of lignin in wood adhesives or for wood modification has received a lot of scientific attention. Despite this, there are only few lignin-derived wood products commercially available. This review provides a summary of the research on lignin application in wood adhesives, as well as for wood modification. The research on the use of uncleaved lignin and of cleavage products of lignin is reviewed. Finally, the current state of the art of commercialization of lignin-derived wood products is presented.

Dielectric and surface properties of wood modified with NaCl aqueous solutions and treated with FE-DBD atmospheric plasma

The hygroscopic and electrical properties of the wood surface of Norway spruce (Picea abies (L.) Karst.) and common beech (Fagus sylvatica L.) were altered by the application of differently concentrated NaCl aqueous solutions. The presence of Na+ and Cl– ions increased the equilibrium moisture content in both woods in environments with a relative humidity of 75% to a nearly saturated state. The electrical resistance of the wood decreased, while the electrical capacitance of the wood increased with increasing amounts of NaCl introduced. Inverse trends were observed for both properties in wood modified with the two most concentrated solutions (18 and 36% molality). Microscopic analysis of the outer layers of the wood samples using scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that the amount of NaCl decreased linearly up to about 1 mm from the modified surface. The presence of Na+ and Cl– ions in wood increased the intensity and improved the homogeneity of the plasma discharge generated during treatment of samples in air at atmospheric pressure. Both modification of wood with NaCl and subsequent treatment with plasma increased the surface roughness of the substrates. Finally, it was shown that the wettability of wood with a waterborne coating was improved after plasma treatment, regardless of the presence of NaCl on the surface. These findings have a good potential not only for the study of surface treatment processes of wood with plasma discharges, but also for other technical applications of lignocellulosic materials.

The heat insulation and smoke suppression effect of M-Si-phosphocarbonaceous catalyzed by metal salt-doped APP silicon gel in situ build in wood

Wood is favored by furniture and decorative materials due to its beautiful color and texture, lightweight and high strength, but the thermal stability and flame retardants of wood have not been well solved. In this paper, metal salt-doped ammonium polyphosphate silicon gel (Cu, Mn/APP/Gel) was trapped in the wood cell wall and cell cavity by vacuum-pressure infusion method and vacuum drying method. Compared with unmodified wood, Cu, Mn/APP/Gel impregnated wood can rapidly enhance the flame retardant and smoke suppression capability of wood due to the catalysis of Cu2+ and Mn2+, and the total heat release rate, heat release rate peak value, mean heat release rate, smoke produce rate, total smoke release, CO and CO2 yield (YCO, YCO2) are obviously reduced. The electronic microscope picture of the burned carbon layer shows that the Cu, Mn/APP/Gel doped wood no longer has a clear and beautiful carbon layer formed by cell structure, but completely forms a whole. It is this dense and firm carbon layer structure that effectively inhibits the thermal decomposition of wood and has a role in flame retardant and smoke suppression. This study proposed an environment-friendly and green scheme for flame retardant modification of wood.

Studying the Performance of Composites Based on Thermally Modified and UV-Treated Wood

To enhance the quality of wood and extend its industrial applications, various methods of wood modification are being developed. It is well known that the thermal treatment of wood may considerably enhance its moisture resistance, reduce its hygroscopicity, and increase its rot proofing. However, reducing the absorptive capacity of wood adversely affects the process of obtaining wood-based composites. Pressure and pressing time increase, which finally increases the cost of the end product. Thus, this study represents the research in how ultraviolet exposure affects the physical properties of wood that has been pre-treated thermally, followed by obtaining a composite. An experimental wood-modifying facility has been developed. We have considered the process of the moisture absorption of the material that has been exposed to thermal modification and UV-radiation. From the experiments conducted, we have found that the UV exposure of wood samples causes an increase in the surface wettability of the thermally modified material. It is found that the most active process of surficial inactivation runs within 60-90 minutes of the UV-exposure of wood. Post-treatment does not result in any considerable changes in the surface wettability. This treatment promotes the increasing adhesion of water-borne binders to the material surface in developing high-strength composites based on modified wood.

Hygroscopic properties of thermally modified false Iroko [Antiaris toxicara (Lesch)

The study investigated the use of thermal modification to improve the hygroscopic properties of False Iroko [Antiaris toxicaria (Lesch)]. Samples of Antiaris toxicara Lesch wood were subjected to thermal modification in a furnace at temperatures of 160, 180 and 200°C for 30 and 60 minutes. Results showed that wood properties were improved with exposure to different temperatures. Subsequent to the thermal process, a colour change from pale yellow to darkish brown was observed progressively with increase in temperature, accompanied by a weight loss in the range of 12.08% to 23.67%. The outcome of these treatments resulted in a decrease in volumetric swelling and increase in dimensional stability of modified wood; this can be attributed to observed decrease in moisture intake. The thermal modification of Antiaris toxicara Lesch wood affected the dimensional stability properties. Thus, due to significant changes via modification carried out on the selected species which is classified as lesser utilized wood species, lesser utilized wood,Antiaristoxicara Lesch wood is recommended for use due to its efficient dimensional stability after modification .
 keywords:, Thermally modified wood ;False Iroko

Встановлення закономірностей дифузії вологи через полімерну оболонку термічно модифікованої деревини

An analysis of the process of thermal modification of wood, which was obtained by a controlled heating process, was done. The unique technological properties (durability, low hygroscopicity and dimensional stability) of thermomodified wood make it possible to use it in various scope. Due to the influence of temperature there are some chemical changes in the structures of the wood cell wall components (lignin, cellulose and hemicellulose). This leads to an increase in density, hardness, improved hydrophobicity (water repellency), thereby reducing their ability to absorb moisture and swell. The products absorb moisture gradually, are less prone to swelling and shrinkage, but still need the elastic coatings application. It is proved that heat-treated wood turns gray over time under the influence of sunlight, and therefore requires additional surface treatment with a coating. Additional protective substances application on the thermo-modified wood products surface promotes dimensional stability and protects against rapid weathering of the surface in open air conditions. The use of transparent coatings and oils does not protect the surface from discoloration during weathering. They are recommended for products are manufactured from thermomodified wood, which are operated away from direct sunlight and rain. The parameters of moisture penetration into wood are mathematically modeled on the basis of the moisture diffusion quasi-stationary equation through the polymer coating on the flat sample surface. The dynamics of moisture content changes in thermally modified wood by different schedules parameters has been experimentally studied. The obtained mathematical relations based on the experimental studies results make it possible to calculate the moisture diffusion coefficient in thermally modified wood in the presence of a polymer shell. It is established that the wax coating application on the surface of the product reduces the moisture diffusion process more than 10 times for surfaces treated at a temperature of 160 °C for 1 hour. That is, such products can be used on objects with high humidity.

Influence of Traditional Wood Surface Modification Methods on Changes in Aesthetic and Resistance Properties

For ages, furniture makers have been using various methods to accelerate the natural process of wood aging, in order to achieve a more sophisticated colour and to provide a uniform appearance for furniture parts replaced during restoration. Nowadays, wood aging is popular due to its aesthetic value associated with naturally aged wood, which can be enjoyed in conjunction with favourable mechanical properties of contemporary wood. Methods of wood surface modification used in wood aging can be divided into mechanical ones, consisting in changing the structure of wooden surfaces (eg. sanding, brushing, paint rubbing or structuring with chisel or other tools) and chemical ones, involving the use of chemical substances to change the colour of wood (eg. greying; application of lye, paint or wood stain; and ammonia fuming). The purpose of our study was to determine the influence of traditional wood modification techniques used in furniture-making − such as: structuring, whitewashing, rubbing, greying, dyeing with potassium permanganate solution and ammonia fuming − on the aesthetic and resistance properties of wooden surfaces (colour, gloss, roughness, abrasion resistance and resistance to scratches). Tests were performed on wood species most frequently used in Poland to produce artificially weathered wood: Scots pine (Pinus sylvestris L.) and common oak (Quercus Sp).

СВЯЗЬ МЕЖДУ СВОЙСТВАМИ ДРЕВЕСИНЫ И ДЕФОРМАТИВНОСТЬЮ ПРИ РАЗЛИЧНЫХ РЕЖИМАХ НАГРУЖЕНИЯ

Modification of wood by pressing makes it possible to obtain a durable material from low-quality wood species. The relationship between the structure of natural and pressed wood and deformability was investigated in the works of B.I. Ogarkov, P.P. Erinsh, V.A. Shamaev, G.K. Gavrilov. Meanwhile, at present wood is subjected to deformation in a plasticized state, the structure and properties of which are different from the structure of natural wood. In this work, an attempt to establish the relationship between the structure of natural and plasticized wood and its main, deformative indicators (stiffness, modulus of elasticity, Poisson's ratio, etc.) has been made . As a result of the experiments, it was found that (according to the results of processing empirical diagrams "deformation - stress") a three-phase nature of deformation of natural birch wood and plasticized with TCL (thermocatalytic cracking liquid) oil was established with the calculation of stiffness indicators; the dependences of the Punch ratio at variable humidity and temperature during the pressing process for constant and variable loading rates were obtained. Hysteresis in wood under tension and compression for natural and plasticized wood has been studied

Environmental Impact of Wood Modification

The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a number of environmental product declarations (EPDs). Using these data, it is possible to determine what the extra impact associated with the modification is. The process of modification results in a life extension of the product, which has implications regarding the storage of sequestered atmospheric carbon in the harvested wood products (HWP) materials’ pool and also extended maintenance cycles (e.g., longer periods between applying coatings). Furthermore, the life extension benefits imparted by wood modification need to be compared with the use of other technologies, such as conventional wood preservatives. This paper analysed the published data from a number of sources (peer-reviewed literature, published EPDs, databases) to compare the impacts associated with different modification technologies. The effect of life extension was examined by modelling the carbon flow dynamics of the HWP pool and determining the effect of different life extension scenarios. Finally, the paper examined the impact of different coating periods, and the extensions thereof, imparted by the use of different modified wood substrates.

Wood Modification as a Tool to Understand Moisture in Wood

Moisture plays a central role in the performance of wood products because it affects important material properties such as the resistance to decomposition, the mechanical properties, and the dimensions. To improve wood performance, a wide range of wood modification techniques that alter the wood chemistry in various ways have been described in the literature. Typically, these modifications aim to improve resistance to decomposition, dimensional stability, or, to introduce novel functionalities in the wood. However, wood modification techniques can also be an important tool to improve our understanding of the interactions between wood and moisture. In this review, we describe current knowledge gaps in our understanding of moisture in wood and how modification has been and could be used to clarify some of these gaps. This review shows that introducing specific chemical changes, and even controlling the distribution of these, in combination with the variety of experimental methods available for characterization of moisture in wood, could give novel insights into the interaction between moisture and wood. Such insights could further contribute to applications in several related fields of research such as how to enhance the resistance to decomposition, how to improve the performance of moisture-induced wooden actuators, or how to improve the utilization of wood biomass with challenging swelling anisotropy.

Macroscopic and Microscopic Modifications of Wood after Debarking of Trees in the South Cameroon

Wounding of trees by debarking has been reported to form a callus tissue. This work aims to investigate macroscopic and microscopic modifications of wood after the removal of barks in Alstonia boonei, Scorodophloeus zenkeri, and Garcinia lucida. Species that are not yet barking were wounded to conducting experimental debarking. The wound was rectangular with 30 cm vertically with a lateral extent of 10 cm. Every three months, there was a follow-up for fifteen months during which the macroscopic and microscopic phenomena were observed and recorded. Microsections of 15–20 μm thickness were taken on a piece of wood from the regenerated and intact wood, with a sledge microtome. Staining of cell walls was done with safranin and fast green to increase contrast in an anatomical slide. Analyzes of the variability of xylem anatomical features were done by semi-automatic measurements using the SpectrumSee digital image analysis software. The speed of recovery of the bark of these three species is 9.04 cm/year for A. boonei, 5.9 cm/year for S. zenkeri, and 3.85 cm/year for G. lucida. The recovery of A. boonei’s bark is the fastest, and it just takes 15 months to heal its wound. Densities of vessels were 8, 38, and 17 per mm², respectively, for the wood of A. boonei, S. zenkeri, and G. lucida before barking. These values increased for A. boonei (26) and G. lucida (20) except for S. zenkeri (25). In all species, the diameter of the vessels has decreased in the regenerated wood. Management practices that enhance the monitoring of sustainable harvesting levels of species and promote alternative plants for the same uses should be considered as part of conservation strategies.

Review of Functional Treatments for Modified Wood

Wood modification is now widely recognized as offering enhanced properties of wood and overcoming issues such as dimensional instability and biodegradability which affect natural wood. Typical wood modification systems use chemical modification, impregnation modification or thermal modification, and these vary in the properties achieved. As control and understanding of the wood modification systems has progressed, further opportunities have arisen to add extra functionalities to the modified wood. These include UV stabilisation, fire retardancy, or enhanced suitability for paints and coatings. Thus, wood may become a multi-functional material through a series of modifications, treatments or reactions, to create a high-performance material with previously impossible properties. In this paper we review systems that combine the well-established wood modification procedures with secondary techniques or modifications to deliver emerging technologies with multi-functionality. The new applications targeted using this additional functionality are diverse and range from increased electrical conductivity, creation of sensors or responsive materials, improvement of wellbeing in the built environment, and enhanced fire and flame protection. We identified two parallel and connected themes: (1) the functionalisation of modified timber and (2) the modification of timber to provide (multi)-functionality. A wide range of nanotechnology concepts have been harnessed by this new generation of wood modifications and wood treatments. As this field is rapidly expanding, we also include within the review trends from current research in order to gauge the state of the art, and likely direction of travel of the industry.